customization for image filerefs respecting xml:base

Hi,

refering to threads 
  [docbook-apps] Best practise: Directories and location of images  
  [docbook-apps] xinclude and images from other directories

many people use Xinclude and a directory structure to order there 
documents and images. As docbook html/fo stylesheets are not aware of 
xml:base attributes yet, you need a customization layer like the one 
attached (i hope, attachments are allowed)

It works fine as M. Sanders reports, but i didn't really test it on 
my own. maybe its of any help for other people.

(of course you have to import the main stylesheet or let this file be 
included by other layers)
 
One feature request for the docbook xsl distribution: At the moment 
there are few lines in Docbook XSL where 
  <xsl:value-of select="@fileref"/>
is used. if replaced by 
  <xsl:apply-templates select="@fileref"/>

everything should work the same because default attribute template 
handles this case.

But you can override the default template by your own. 
This would reduce my customization layer a lot and would make it much 
more easier to write different layers.

kind regards,
janning